1. Field of the Invention
This invention relates to a method of and a structure for cooling integrated circuit devices. More particularly, it relates to micro heat pipes formed in an integrated circuit chip, a method of cooling integrated circuits using micro heat pipes, and a method of forming the micro heat pipes.
2. Prior Art
As the size of electronic components decreases and the concomitant component density increases, integrated circuits tend to form local regions on the semiconductor device that produce relatively large amounts of heat. These hot spots can degrade device performance and can lead to device failure. It would therefore be advantageous to conduct this heat from regions of a semiconductor chip generating relatively large amounts of heat to regions of the chip producing relatively small amounts of heat. In this way, the heat generated in an integrated circuit is spread more evenly throughout the chip.
Cotter described very small, micro heat pipes for cooling microelectronic devices. Cotter, T. P., 1984, "Principals and Prospects of Micro Heat Pipes," Proc. 5th Int'l Heat Pipe Conf., Tsukuba, Japan, pp.328-335. He defined a micro heat pipe as "one so small that the mean curvature of the vapor-liquid interface is necessarily comparable in magnitude to the reciprocal of the hydraulic radius of the total flow channel." In practical terms, a micro heat pipe is a wickless, non-circular channel with a diameter of 10-500 micrometers and a length of about 10-20 millimeters.
Cotter proposed micro heat pipes for cooling the volumetric heating produced in a parallel-processing microelectronic component. The evaporator portion of the heat pipe would be an integral part of the device. Heat would be removed from within the device by an array of micro heat pipes.
Cotter derived an approximate theoretical result for the maximum heat transport capability, q.sub.m of a micro heat pipe. For a micro heat pipe with an equilateral triangular shape with sides 0.2 mm, length 10 mm, and an optimum amount of methanol as the working fluid, Cotter predicted a q.sub.m of 0.03 watts. He reasoned that, when used in a solid in an array of parallel pipes (about 10% by volume), these micro heat pipes could provide a few tens of watts per cubic centimeter of cooling.
Besides the difficulties of manufacturing, cleaning and filling these micro heat pipes (Cotter believed that existing micro-mechanical technology as of 1984 could overcome these problems), the micro heat pipe is very sensitive to percent fill of the working fluid. The liquid-vapor interface changes continually along the pipe, and care must be exercised to ensure proper wetted conditions without flooding the micro channels.
It would therefore be advantageous to provide a micro heat pipe that is relatively easy to construct. It would also be advantageous to provide a controllable method of charging a micro heat pipe with a cooling medium.